Emissive Image Substrate Marking, Articles Marked With An Emissive Image, and Authentication Methods Involving The Same

ABSTRACT

A system for printing and emissive image on a substrate that includes red, green, and blue additive-color emissive inks configured to be printed to a substrate using an ink printer device intended for use with subtractive-color ink. An image to be printed can be converted to color negative form prior to printing using the subtractive-color ink printer. The system may include a subtractive-color ink printer intended for use with subtractive-color ink cartridges. The system may also include a computer device programmed to convert an image to a color negative form.

RELATED APPLICATION DATA

This application is a continuation of U.S. application Ser. No.12/911,175, filed Oct. 25, 2010, and titled “Emissive Image SubstrateMarking, Articles Marked With An Emissive Image, and AuthenticationMethods Involving the Same,” which application is a continuation of Ser.No. 10/818,058, filed Apr. 5, 2004, and titled “Methods and InkCompositions for Invisibly Printed Security Images Having MultipleAuthentication Features,” which application claims the benefit ofpriority of U.S. Provisional Patent Application Ser. No. 60/460,599,filed Apr. 4, 2003, and titled “Methods and Ink Compositions forInvisibly Printed Security Images Having Multiple AuthenticationFeatures.” Each of these applications is incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of securityprinting and more particularly to ink-jet printing of color fluorescentindicia and authentication of articles such as documents for securitypurposes. In particular, the present invention is directed to methodsand ink compositions for invisibly printed security images havingmultiple authentication features.

BACKGROUND OF THE INVENTION

There is a need for improved methods and materials which extend thecurrent knowledge and applications to create practical, cost-effectivesolutions for the security field. Security of currency, identificationdocuments, product brands, and other materials has become anincreasingly important concern for government and industry. As theft andfraud increase, security protocols must evolve to detect and prevent theincreasingly more sophisticated and technologically based methods ofcounterfeiting and product diversion.

While there are many different methods and techniques used to providesecurity, an approach that uses more than one type of security ispreferable. In such an approach, multiple security discriminationfeatures are examined.

If one or more of the individual features is compromised, the securityof the system as a whole remains intact. Such methods using multiplediscrimination features are taught, for example, in U.S. Pat. No.5,418,855 to Liang et al., assigned to the same assignee as the presentinvention.

The use of fluorescent materials such as ultraviolet (UV)-fluorescent,infrared (IR)-fluorescent, or near-infrared (NIR)-fluorescent materialsfor security markings is well known. The use of fluorescent materialsallows the user to easily detect the security markings by irradiation ofthe marks with a suitable UV or NIR/IR light source. The fact thatfluorescent materials emitting light in the visible spectrum can bedetected by simple examination has made them easier to counterfeitand/or duplicate. However, this fact is also an advantage in that theuser can easily and quickly authenticate the security marks.

While there are important distinctions between the uses ofUV-fluorescent and IR-fluorescent materials that emit in the IR(infrared) and/or NIR (near-infrared) range, there are also advantagesand disadvantages in the use and applicability of the latter materials,e.g., the NIR/IR emissions are not detectable by simple visualobservation. As with UV fluorescence, this can be advantageous for someapplications, but disadvantageous for other applications.

Many fluorescent materials are also easily detectable under illuminationin the visible portion of the spectrum, but “invisible” fluorescentmaterials are known, i.e., those materials that are not visuallydetectable under ordinary white-light, but emit detectable fluorescentlight when illuminated by light outside the visible spectrum.

Inkjet printing is a versatile technique in that it can deliver smallvolumes of liquid inks with a variety of different compositions that canbe specifically formulated for many different applications. Inkjetprinting methods have been used successfully to print on a variety ofdifferent substrates, including many types of paper, from cardboard tonewsprint, many types of fabric, and various other polymers, such asplastic. These characteristics make inkjet printing an excellent methodof delivery for many types of materials, including fluorescent indiciafor security marking. Color inkjet printers, however, typically use setsof subtractive-color inks (typically 3-6 inks in a set), combined inaccordance with a corresponding color space. Such inks are generally notfluorescent and are intended to be visible under ordinary white-lightillumination (illumination in the visible portion of the spectrum,having wavelengths generally in the range between 400 nm and 700 nm).

While fluorescent security indicia have been widely used in currency andin passports and other identification documents, most of suchapplications have used single fluorescent colors or simple combinationsof individual colors, which have often been visible under ordinarywhite-light illumination. Thus, security applications using suchfluorescent materials may not provide the level of security desired forcertain applications.

The foregoing shortcomings and problems of the prior art are improvedupon, and further advantageous solutions are provided by the presentinvention.

SUMMARY OF THE INVENTION

In one implementation, an emissive image printing system for printing animage on a substrate, the image being emissively perceptible, isprovided. The system includes a red additive-color emissive ink having ared emissive component with a dominant emissive wavelength between about590 nanometers and about 680 nanometers when exposed to an excitationenergy, the red emissive component being substantially invisible underillumination within the visible spectrum when the red additive-coloremissive ink is printed as part of an image indicia on a substrate; agreen additive-color emissive ink having an green emissive componentwith a green dominant emissive wavelength between about 500 nanometersand about 550 nanometers when exposed to the excitation energy, thegreen emissive component being substantially invisible underillumination within the visible spectrum when the green additive-coloremissive ink is printed as part of the image indicia; and a blueadditive-color emissive ink having an blue emissive component with ablue dominant emissive wavelength between about 420 nanometers and about480 nanometers when exposed to the excitation energy, the blue emissivecomponent being substantially invisible under illumination within thevisible spectrum when the blue additive-color emissive ink is printed aspart of the image indicia, the red, green, and blue additive-coloremissive inks being configured to be printed to a substrate using an inkprinter device intended for use with subtractive-color ink.

In another implementation, an emissive image printing system forprinting an image on a substrate, the image being emissivelyperceptible, is provided. The system includes a red additive-coloremissive ink having a red emissive component with a dominant emissivewavelength between about 590 nanometers and about 680 nanometers whenexposed to an excitation energy, the red emissive component beingsubstantially invisible under illumination within the visible spectrumwhen the red additive-color emissive ink is printed as part of an imageindicia on a substrate; a green additive-color emissive ink having angreen emissive component with a green dominant emissive wavelengthbetween about 500 nanometers and about 550 nanometers when exposed tothe excitation energy, the green emissive component being substantiallyinvisible under illumination within the visible spectrum when the greenadditive-color emissive ink is printed as part of the image indicia; ablue additive-color emissive ink having an blue emissive component witha blue dominant emissive wavelength between about 420 nanometers andabout 480 nanometers when exposed to the excitation energy, the blueemissive component being substantially invisible under illuminationwithin the visible spectrum when the blue additive-color emissive ink isprinted as part of the image indicia, wherein the red, green, and blueadditive-color emissive inks are configured to be printed to a substrateusing an ink printer device intended for use with subtractive-color ink;a computer device programmed to convert an image to be printed using thered, green, and blue additive-color emissive inks to a color negativeform; and a subtractive-color ink printer intended for use withsubtractive-color ink, wherein the red, green, and blue additive-coloremissive inks are configured to be printed to a substrate using thesubtractive-color ink printer.

In yet another implementation, an emissive image printing system forprinting an image on a substrate, the image being emissivelyperceptible, is provided. The system includes a subtractive-color inkprinter intended for use with subtractive-color ink; a redadditive-color emissive ink having a red emissive component with adominant emissive wavelength between about 590 nanometers and about 680nanometers when exposed to an excitation energy, the red emissivecomponent being substantially invisible under illumination within thevisible spectrum when the red additive-color emissive ink is printed aspart of an image indicia on a substrate, the red additive-color emissiveink included in a container configured to replace a cyan-coloredsubtractive ink container of the subtractive-color ink printer; a greenadditive-color emissive ink having an green emissive component with agreen dominant emissive wavelength between about 500 nanometers andabout 550 nanometers when exposed to the excitation energy, the greenemissive component being substantially invisible under illuminationwithin the visible spectrum when the green additive-color emissive inkis printed as part of the image indicia, the green additive-coloremissive ink included in a container configured to replace amagenta-colored subtractive ink container of the subtractive-color inkprinter; a blue additive-color emissive ink having an blue emissivecomponent with a blue dominant emissive wavelength between about 420nanometers and about 480 nanometers when exposed to the excitationenergy, the blue emissive component being substantially invisible underillumination within the visible spectrum when the blue additive-coloremissive ink is printed as part of the image indicia, the blueadditive-color emissive ink included in a container configured toreplace a yellow-colored subtractive ink container of thesubtractive-color ink printer; and a computer device programmed toconvert an image to be printed using the red, green, and blueadditive-color emissive inks to a color negative form and to use thesubtractive-color ink printer to print the image using the colornegative form and the red, green, and blue additive-color emissive inks.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

For the purpose of illustrating the invention, the drawings show a formof the invention that is presently preferred. However, it should beunderstood that the present invention is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a conventional CIE 1931 chromaticity diagram showingapproximate regions generally identified with some common color names;

FIG. 2 is a CIE 1931 chromaticity diagram illustrating gamuts ofconventional subtractive-color and additive-color systems;

FIG. 3 is a black and white CIE 1931 chromaticity diagram illustrating acolor region of red emissions of fluorescent ink embodiments made inaccordance with the invention;

FIG. 4 is a black and white CIE 1931 chromaticity diagram illustrating acolor region of green emissions of fluorescent ink embodiments made inaccordance with the invention;

FIG. 5 is a black and white CIE 1931 chromaticity diagram illustrating acolor region of blue emissions of fluorescent ink embodiments made inaccordance with the invention;

FIG. 6 is a black and white CIE 1931 chromaticity diagram illustrating acolor gamut of emissions of fluorescent ink embodiments made inaccordance with the invention;

FIGS. 7A-7C show black and white versions of color separation negativeimages prepared from a type of full-color image that may be used withthe invention;

FIG. 8 shows a black and white image of a type that may be used with theinvention; and

FIG. 9 is a black and white CIE 1931 chromaticity diagram illustrating acolor gamut of emissions of fluorescent ink embodiments made inaccordance with another quantum dot embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention described in detail are intended to beillustrative, and the invention is not limited to the materials,conditions, compositions, or other parameters shown in theseembodiments.

Throughout this specification and the appended claims, the term“invisible” means substantially undetectable to the unaided human eyeunder illumination by light in the visible portion of the opticalspectrum (generally considered as having wavelengths in the rangebetween about 400 nm and about 700 nm), also referred to as “whitelight.”

As background for the following description of the invention, FIG. 1shows a conventional CIE 1931 chromaticity diagram illustratingapproximate regions generally identified with some common names of huesas listed in TABLE 1. TABLE 1 shows the hue designations and thereference numeral corresponding to each hue. FIG. 1 is based on thearticle by Kenneth L. Kelly, “Color Designations for Lights,” Journal ofthe Optical Society of America, vol. 33 (1943) pp. 627-632.

TABLE 1 Reference Numerals Corresponding to Hues in FIG. 1 Referencenumeral Hue 1 Illuminant Area 2 Yellowish Green 3 Yellow-Green 4Greenish Yellow 5 Yellow 6 Yellowish Orange 7 Orange 8 Orange Pink 9Reddish Orange 10 Red 11 Purplish Red 12 Pink 13 Purplish Pink 14 RedPurple 15 Reddish Purple 16 Purple 17 Bluish Purple 18 Purplish Blue 19Blue 20 Greenish Blue 21 Blue-Green 22 Bluish Green 23 Green

Those skilled in the art will understand that the boundaries delineatingnamed hue regions in the chromaticity diagram in FIG. 1 are somewhatarbitrary, and for the purpose of describing the present invention serveonly to indicate qualitatively and approximately where various hues arelocated in the continuous visual color space represented by thechromaticity diagram, without reproducing the chromaticity diagram incolor. Full-color reproductions of the CIE 1931 chromaticity diagram arereadily available in many published references on color theory andcolorimetry, including the World Wide Web URL,http://www.efg2.com/Lab/Graphics/Colors/Chromaticity.htm.

The “horseshoe” shaped line 30 is the spectral locus. Wavelengths innanometers (nm) are shown around the edge. The straight line 40connecting the endpoints of the “horseshoe” curve is known as thenon-spectral “line of purples.” Coordinates x and y measured along theabscissa and ordinate axes respectively are related to tristimulusvalues X, Y, and Z by the relationships x=X/(X+Y+Z); y=Y/(X+Y+Z);z=Z/(X+Y+Z); and x+y+z=1.

FIG. 2 is a CIE 1931 chromaticity diagram schematically illustratingapproximate gamuts of conventional subtractive-color and additive-colorsystems, i.e., the limited portions of the whole chromaticity diagramthat can be reproduced in those systems. Region 50 represents theapproximate gamut of subtractive-color inks commonly used in colorprinting. The triangular region 60 represents the approximate gamut ofthe RGB system of additive colors commonly used for emissive displays.It will be apparent that the regions 50 and 60 do not coincide, so thatcolors of an image that may be represented on an RGB computer monitor,for example, may not match colors of the same original color imageprinted on a color printer, and there are colors that are achievable inone gamut that are not achievable at all in the other gamut.Nevertheless, there are many applications for which the color-renderingcapabilities of both systems are entirely satisfactory.

A problem that occurs when one tries to print a color image withfluorescent inks may be readily understood by reference to FIG. 2. Thenormal subtractive-color inks commonly used in color printing are calledsubtractive colors because their perceived colors are determined by thelight that they absorb or subtract from the incident light. The“subtractive primary colors” commonly used in color printing are cyan,yellow, magenta (and sometimes black). In printing colors of hues otherthan cyan, yellow, magenta, these subtractive primary colors combine bycombining their absorptions. Thus, for example to print a green color,cyan and yellow inks are combined. Together, the cyan and yellow inksabsorb light of wavelengths corresponding to red and blue, leaving onlygreen light to be reflected from the printed ink.

However, the colors exhibited by fluorescent inks are emissive colors,which combine in an additive manner, not a subtractive manner to producea resultant emission. Furthermore, no combination of non-fluorescentsubtractive-color inks would create a fluorescent color, norspecifically an invisible image that is fluorescent. This problem wouldnot be solved by merely substituting fluorescent inks with cyan, yellow,and magenta fluorescent emission even if such inks were all readilyavailable. Therefore, the conventional method used to print color imageswith a color printer (for example, an inkjet printer) cannot be used.

The present invention includes methods for printing invisible imageswith specially formulated inks whose fluorescent emissions can becombined to form full-color, high resolution, images. “Full color”image, as used in this context, is defined as an image that containscolors that cannot be created by a single chromophore, but instead arecreated with combinations of chromophores. The meaning of “highresolution” varies, to some extent, as a function of the application inwhich the image is to be used. In general, resolutions greater than 400dpi will suffice for the full-color, high resolution images of thepresent invention.

The images produced can be used for displaying information, fordecoration, for marking an article with indicia for authentication, orfor other purposes. Thus, a method for marking an article with imageindicia includes providing a plurality of inks that produce fluorescencecolors when exposed to suitable excitation energy (often illuminationoutside the visible spectrum), separating colors of the image indiciainto a plurality of image levels in accordance with the fluorescencecolors of the inks, and printing each image level in mutual registrationon the article using the corresponding ink. Indicia printed with each ofthe inks are substantially invisible under illumination within thevisible spectrum. As suggested above, the inks may comprise inkjet inksand the printing may be performed using an inkjet print head. Additionalinformation concerning inkjet printers and printing is described in U.S.Pat. No. 6,149,719, which is incorporated herein by reference in itsentirety.

Generally, no modification is needed of an inkjet printer intended foruse with subtractive-color ink container (e.g., reservoir or cartridge),and such a printer can be used to print the invisible full-colorfluorescent images. The printing is accomplished by converting images(or any indicia) to be printed to a color negative form and by replacingeach subtractive-color ink container with a container containing one ofthe plurality of inks having a plurality of fluorescence colors.Specifically, each subtractive-color ink container is replaced by acontainer containing an ink of its complementary color. The cyan inkcontainer is replaced with a container containing ink having a redfluorescence color. The magenta ink container is replaced with acontainer containing ink having a green fluorescence color. The yellowink container is replaced with a container containing ink having a bluefluorescence color. In the case of inkjet printers that use reservoirsinstead of cartridges or other containers, the reservoir is merelycleaned, using the process described below, and then is refilled withthe complementary fluorescent ink. All three of the fluorescent inks maybe inks that are invisible under ordinary illumination within thevisible spectrum.

It will be recognized that the order of steps in the method describedabove may be varied. For example, the color separating may be done atany time, including a time just before providing the fluorescent inks byinstalling or filling their ink containers. Or the printer may beprepared by providing the fluorescent ink containers before the colorseparation is done.

Color separation and conversion of image data to a negative form may beperformed with commercially available computer software, such as Adobe®Photoshop® or Adobe® PhotoShop® Elements (both available from AdobeSystems, Inc. of San Jose, Calif.), Corel® Photo-Paint™ (available fromCorel Corp. of Ottawa, Ontario, Canada), or ArcSoft® PhotoStudio®(available from ArcSoft, inc. of Fremont, AC), or equivalentphoto-editing software.

Those skilled in the art will recognize that visibility or invisibilityof a printed ink may depend to some extent on the substrate on which itis printed. For example, a fluorescent ink containing a substantialamount of white pigment may often be printed on white paper and yet beinvisible under ordinary illumination within the visible spectrum. Thesame ink would not be invisible under white light if printed on a blackpaper.

Many color inkjet printers use a CYMK system including cyan, yellow,magenta, and black inks. For such printers, the black-ink print head maybe disabled, e.g., by replacing a black ink cartridge with a blankcartridge. Alternatively, for some applications, a black ink may beprovided along with the inks that produce a plurality of fluorescencecolors under illumination outside the visible spectrum (emissive oradditive colors). The colors of the image indicia are separated into ablack image level and the fluorescence-color image levels, and theprinting is done as described above, including the un-reversed blackimage level. That is, all of the subtractive colors except black areconverted to their color negatives, and all the ink colors except blackare replaced by their color-complementary emissive inks (red for cyan,green for magenta, and blue for yellow, respectively). The base of theblack ink and the printing of the black image level are user-optional.

Also, before using an inkjet printer with fluorescent ink containerssubstituted in the manner described above, it is advisable to clean theprinter to remove any residue of non-fluorescent inks remaining fromprevious use of the inkjet printer before inserting the fluorescent inkcontainers. Similarly, as referenced above, when the inkjet printer usesrefillable reservoirs to contain the ink, then it is generally desirableto clean the reservoirs to remove residual non-fluorescent inks. Asuitable cleaning composition for this purpose consists of a mixture (byweight % (w/w)) of 2-propanol [67-63-0]: 71.00%;N-methyl-2-pyrrolidinone [872-50-4]: 4.00%; butyl carbitol [112-34-5]:5.00%; and diethylene glycol [11-46-6]: 20.00%.

The set of fluorescent inks includes a set of emissive colors that arethe additive primary colors, red, green, and blue. A suitably weightedcombination of these three colors combines to create white emission. Forsome applications, it may be useful to use combinations of only two ofthe three additive primary colors, such as red and green, red and blue,or blue and green. For example, invisible red-green fluorescentanaglyphs that combine to make a stereographic image when viewed throughan appropriate filter over each eye may be printed using red and greensub-images. For another example, many colors may be obtained by printingred and green fluorescent inks on a blue fluorescent substrate.

However, to create full-color fluorescent images on a non-fluorescentsubstrate, the full set of three emissive colors is used, including thered, blue, and green additive primary colors. Since black “color”corresponds to no emission in an emissive or additive color system,black content in a full-color image may be handled for many applicationsby omitting the black separation image of a four-color additive-colorseparation. For other applications, such a black separation image may beprinted without conversion to a negative image layer as described above.

To create a “black” color on a substrate that contains opticalbrighteners, an ink containing one or more fluorescent quenchers can beused to quench the white-blue fluorescent optical brightening effectcreated by the optical brighteners. This is accomplished by using anink, possibly in place of the black cartridge of the inkjet printer,that contains one or more fluorescent quenchers, such as acrylamide,various amines, halogens, bromobenzene, various chlorides andchlorinated compounds, cobalt (Co2+) ions, copper (Cu2+) ions,dimethylformamide, disulfides, ethers, hydrogen peroxide, imidazole,histidine, iodide, nickel (Ni2+) ions, nitro compounds, nitromethane,nitroxides, nitric oxide, various olefins, oxygen, other peroxides,pyridine, various quinones, silver (Ag+) ions, thallium (Ti+) ions,thiocyanate, and/or other known quenchers of fluorescence. Thesematerials may be used separately or in combination to elicit the desiredquenching effect. Then, a suitable clear-coat, binder, or other materialthat prevents the quenching of fluorescent inks can be subsequentlyprinted over the quenched “black” areas to allow printing of additionalfluorescent colors.

For certain applications, it may be desirable to create an image usingthe fluorescent inks of the present invention on a substrate that doesnot include optical brighteners. By eliminating the blue colorationprovided by the optical brighteners in the substrate a non-emissivebackground “black” color is created, making it easier to create desiredcolors using various combinations of fluorescent inks. Photographicpapers of the matte heavyweight photopaper type (part # S041257)available from Epson having optical brighteners on only one surface canbe satisfactorily used as a substrate for receiving an image of thepresent invention, in this case the side that does not contain opticalbrighteners would be used as the “black” or non-emissive background. Inselected cases, it may be desirable to use the fluorescent quenchersdiscussed above together with a substrate that lacks opticalbrighteners.

The fluorescent inks of the present invention may be used to create“inverse” barcodes. Inverse barcodes consist of bands of ink spaced fromone another by portions of the substrate that lack ink. Thus, in inversebarcodes, the ink provides the “white” portion of the barcode patternand the “black” portions are the sections between where the ink isprinted. The “white” portions of the barcode may be printed with thewhite ink of the present invention, or may be printed with a color ink.The “black” portion of the barcode may be unprinted portions of a darksubstrate or a substrate without optical brighteners or may be theportion of a substrate that has been coated with fluorescent quenchersof the type described above.

In terms of the wavelengths of the fluorescent emissions stimulated byUV excitation energy, the red component of the emissive colors may havea dominant emissive wavelength between about 590 and about 680nanometers. The green component of the emissive colors may have adominant emissive wavelength between about 500 and about 550 nanometers.The blue component of the emissive colors may have a dominant emissivewavelength between about 420 and about 480 nanometers.

FIGS. 3-5 are CIE 1931 chromaticity diagrams illustrating the threecolor regions of fluorescent emissions of the UV fluorescent inkembodiments made in accordance with the invention. FIG. 3 shows thecolor region 70 of red emissions of fluorescent ink. FIG. 4 shows thecolor region 80 of green emissions of fluorescent ink. FIG. 5 shows thecolor region 90 of blue emissions of fluorescent ink. FIG. 6 illustratesthe resulting color gamut 100 of emissions of fluorescent inkembodiments made in accordance with the invention.

Another way of characterizing the emissive colors is by numericalcoordinates in a CIE chromaticity diagram. For example a useful set ofemissive colors includes a red component having CIE 1931 chromaticitycoordinates describing a plane comprising the following (X,Y coordinate)points of approximately, (+/−0.05): (0.48, 0.22) (0.48, 0.43), and(0.67, 0.26); a green component having CIE 1931 chromaticity coordinatesof (0.14, 0.42) (0.12, 0.72), and (0.43, 0.46); and a blue componenthaving CIE 1931 chromaticity coordinates (0.16, 0.10) (0.15, 0.38), and(0.30, 0.15).

The particular red, blue, and green additive primary-color hues may becompatible with an RGB standard, such as the older International RadioConsultative Committee (CCIR) Standard 601; the InternationalTelecommunications Union, Radiocommunications Sector (ITU-R) “Studioencoding parameters of digital television for standard 4:3 and widescreen 16:9 aspect ratios” Standard BT.601; the Electronic IndustriesAssociation (EIA) Standard RS-170A; the Video Electronics StandardsAssociation (VESA) Standard 1.2; or their successor standards andversions.

The source images used in methods of the present invention may becreated by many means, such as photography (including direct digitalphotography), scanning an image recorded in visible light, scanning ahard-copy original image, scanning a hard-copy photograph, and creatingart with computer graphics software. The resulting images can beprovided in the form of one or more computer-readable files, which maybe in a standard image file format, such as a bitmap file format, astandard TIFF file format, or a standard JPEG file format. Proprietaryimage file formats may also be used with appropriate computer softwaredesigned to operate on them. The images may be provided in the form offiles carried by machine-readable media such as magnetic computerdiskettes, digital magnetic tape, CD-ROM's, etc. Those skilled in theart will recognize that using images stored on such media facilitate theoperations of separating colors of the image into a plurality of imagelevels and forming the color negative versions of those levels whenthose operations are performed by using a suitably programmed computer.Some printers, especially those designed for photographic printing, mayalso have built-in capability for performing the operations ofseparating colors of the image into a plurality of image levels and/orforming the color negative versions of those levels.

FIGS. 7A-7C show color separation negative images prepared in accordancewith methods of the present invention from a type of full-color imagethat may be used with the invention. FIG. 8 shows a black and whiteversion of a similar image, as it would be printed by a black-and-whitetechnique described hereinbelow.

The images shown in FIGS. 7A-7C were prepared by separating the originalfull-color image into three levels or layers: cyan, magenta, and yellow(omitting a black layer) and converting each layer to its negative.Thus, FIG. 7A shows a negative of a cyan color-separation layer. Thenegative image shown in FIG. 7A is used to print with invisiblered-fluorescent ink. Similarly, FIG. 7B shows a negative of a magentacolor-separation layer, and the negative image shown in FIG. 7B is usedto print with invisible green-fluorescent ink. FIG. 7C shows a negativeof a yellow color-separation layer, and the negative image shown in FIG.7C is used to print with invisible blue-fluorescent ink. The threelayers are, of course, printed in mutual registration by the printer.

A related variation of this method may be used to print an image likethe one in FIG. 8 with fluorescent ink that is invisible under ordinaryillumination within the visible spectrum, and has white fluorescentemission under non-visible illumination. Such inks are describedhereinbelow, in the section titled “Ink Compositions.” The originalblack and white image is converted to a negative image and the negativeimage printed with a white-fluorescent ink on a non-fluorescentbackground, which may be black. The resultant fluorescent image closelymatches FIG. 8.

For many security applications, it is desirable to use images of humansubjects for identification purposes and especially desirable to useimages containing various natural human skin tones. Therefore, it isdesirable that the methods and apparatus for printing invisiblefull-color fluorescent images have a color gamut including a range ofhues corresponding to natural human skin tones. The methods andapparatus of the present invention achieve such a color gamut. If thefull-color fluorescent image corresponding to the combination of FIGS.7A-7C could be reproduced here, the successful reproduction of naturalhuman skin tones would be apparent. Examples of human skin tonesachievable by the present invention are the light skin tonecorresponding to RGB values of about (190, 147, 127) or (205, 163, 144)and the dark skin tones corresponding to RGB values of about (92, 67,52) or (129, 96, 82). Similar skin tones are described in terms of thehue/saturation/value (HSV) system as about (18.7, 0.298, 0.804) and(17.9, 0.364, 0.506) respectively. A wide variety of other natural humanskin tones are included in the color gamuts realized by variousembodiments of the present invention.

Passport photographs are a common example of identification images, andthe images made in accordance with the present invention may be made informats that fulfill the official format requirements of a passportphotograph. Thus, an invisible color image of a passport holder could beincluded in a passport. Such an invisible image could be printedadjacent to the normal visible photograph of the passport, or could beprovided alone. Observing the invisible full-color-fluorescent imagewith UV light, for example, would allow ready comparison with thevisible photograph and with the person actually presenting the passport.Any discrepancy among the three, such as substitution of a newphotograph matching an illegitimate passport carrier, would be readilydetected.

Passports are just one of many identity authentication articles that mayinclude an image made in accordance with the present invention. Theauthentication images, features and methods of the present invention maybe used on virtually any article having a surface on which on which animage can be provided.

The passport example illustrates a general method whereby image indiciaprinted on an article using the present invention may be authenticated.In this method, the article is illuminated with light outside thevisible spectrum to display resultant color image indicia by emission offluorescent light having the several colors of fluorescence describedabove, and the resultant color image indicia are compared with coloredreference indicia or with another reference, such as the human subjectin this passport example.

The comparisons with known reference images that are made toauthenticate an article on the basis of the printed invisible colorfluorescent images may be visual comparisons as in the simple passportexample above or may be comparisons made automatically by machine, e.g.,by a scanner or by a suitably programmed computer-based system having acolor digital camera as an input. Either visual or automatic comparisonscan include a step of recording the resultant color image indiciadisplayed by emission of fluorescent light having the plurality offluorescence colors. This recording may be one function of the colordigital camera. In automatic comparison, the programmed computer isresponsive to signals from the color digital camera or otherlight-sensing detector capable of distinguishing colors. In cases wherethe fluorescent emission is other than in the visible spectrum, e.g.,NIR, IR or UV, then machine detection and comparison will be a necessarystep in the process.

Capturing, recording and/or comparison of the colored fluorescent imagesmay be improved by passing the fluorescent light through an opticalfilter before comparing the fluorescent color image indicia with coloredreference indicia. The optical filter may be used to selectively blocklight according to criteria based on specific light wavelength(s), lightwavelengths above a first predetermined wavelength limit, lightwavelengths below a second predetermined limit, a bandwidth range oflight wavelengths, light having a range of colors, and fluorescent lightemitted by one or more known fluorescent chromophores. The latter typeof filter is discussed further hereinbelow in connection with maskingmethods.

Ink Compositions

Ink compositions suitable for use in accordance with the presentinvention are described first in terms of a general ink composition, andthen by specific examples. Throughout this specification and theappended claims, the terms “fluorophore” and “fluorescent chromophore”are used synonymously to mean a molecule that produces a fluorescentemission when irradiated with light at a suitable excitation wavelength(not necessarily in the visible spectrum), a composition exhibitingfluorescence when suitably irradiated, or a compound such as asemiconductor nanocrystal or quantum dot exhibiting fluorescence whensuitably irradiated. While the fluorescent emission occurs with respectto image indicia applied to an article when exposed to suitableexcitation energy, discussion of such emission herein is not intended todefine or limit in any way whether or not the inks of the presentinvention, when in liquid form in a container, do or do not producefluorescent emission when exposed to suitable excitation energy.

A general ink composition suitable for the present invention isdescribed below. All percentages are by weight unless otherwisespecified. Ranges are provided where the component is dependent on thespecific printing system and materials used. Various fluorophores, e.g.,IR fluorescent components with different excitation and emissioncharacteristics, such as UV excitation to IR emission, IR excitation toUV emission, UV excitation to IR and visible emission, and/or IRexcitation to visible and IR emission, may be combined or usedseparately depending on the effect desired. Numbers shown in brackets inthe compositions listed below are CAS numbers identifying specificcomponent materials. Fluorophores used for the methods of this inventionmay include substances and chemical compositions as described in U.S.Pat. No. 4,642,526 to Hopkins, and/or U.S. Pat. No. 5,837,042 to Lent etal., the entire disclosures of which are hereby incorporated byreference.

In the most general sense, the ink composition of the present inventioncontains, by weight % (w/w), distilled or deionized water: 0-95%; abiocide: 0 to 3.0%; a non-ionic surfactant: 0 to 1.0%; organichumectants: 0 to 40%; ethanol: 0 to 40%; propanol: 0 to 40%; buffersalts: 0 to 20.0%; fluorophore pigment or dye: 0 to 20%, including, asthe fluorophore pigment or dye or as an additional authenticationfeature, a microparticle, quantum dot or other component: 0 to 15%. Forthe red, green and blue emissive inks, the fluorophore pigment or dyeused is complementary, respectively, to cyan, magenta and yellow colorsof the subtractive inks.

Somewhat more specifically, the general ink composition contains, byweight % (w/w), distilled or deionized water: 0 to 95.0%; a biocide: 0to 3.0%, such as Proxel GXL (9.3% 1,2-benzisothiazolin-3-one (CAS#[2634-33-5]) (available from Zeneca AG Products, Inc. of Wilmington,Del.); N-methyl-2-pyrrolidinone [872-50-4]: 0 to 20.0%; non-ionicsurfactant, e.g., Surfynol 440 [9014-85-1]: 0 to 1.0%; butyl carbitol[112-34-5]: 0 to 30.0%; glycerol [56-81-5]: 0 to 40.0%; diethyleneglycol [11-46-6]: 0 to 40.0%; 2-pyrrolidinone: 0 to 20.0%; polyethyleneglycols: 0 to 40.0%; ethanol: 0 to 40.0%; propanol: 0 to 40.0%; otheranionic, cationic, and non-ionic surfactants: 0 to 15.0%; buffer salts:0 to 20.0%; fluorophore: 0 to 20.0%, with optional semiconductornanocrystal, microparticle or other component: 0 to 15.0%. Typicalconventional buffer salts include borax, sodium carbonate, and sodiumphthalate.

The following examples describe representative ink formulations for usewith the BJC-6000 series; BJC-3000 series; S-400 series; S-450 series;and/or the MultiPASS C755 Canon printers. These printer types are listedas examples only; this list is not meant to exclude any specific typesof inkjet printers, as this invention and the specific ink formulationsdisclosed may be modified to work with virtually any type of inkjetprinter.

Example 1

An invisible red-fluorescent ink was formulated by mixing 1-propanol[71-23-8]: 40.50%; denatured ethanol [64-17-5]: 30.00%;N-methyl-2-pyrrolidinone [872-50-4]: 5.00%; butyl carbitol [112-34-5]:6.00%; diethylene glycol [11-46-6]: 16.00% and red fluorophore, e.g.,Maple Red core shell Evidots (SG-CdSe—ZnS—Na-Tol-05-620-04, availablefrom Evident Technologies, Inc., Troy, N.Y.): 2.50%. Angstrom SC-25,(available from Angstrom Technologies, Inc. of Erlanger, Ky.) issuitable as a substitute for the red fluorophore in this ink.

Example 2

An invisible green-fluorescent ink was formulated by mixing deionizedwater: 70.20%; Proxel GXL [2634-33-5]): 0.10%; N-methyl-2-pyrrolidinone[872-50-4]: 4.00%; Surfynol 440 [9014-85-1]: 0.40%; butyl carbitol[112-34-5]: 6.00%; glycerol [56-81-5]: 8.00%; diethylene glycol[11-46-6]: 8.00%; and green fluorophore, e.g., Catskill Green core shellEvidots (SG-CdSe—ZnS-Tol-540-04, available from Evident Technologies,Inc., Troy, N.Y.): 3.30%. Angstrom SC-4, SC-24, SC-19, (available fromAngstrom Technologies, Inc. of Erlanger, Ky.) is also suitable as asubstitute for the green fluorophore in this ink.

Example 3

An invisible blue-fluorescent ink was formulated by mixing deionizedwater: 71.00%; Proxel GXL [2634-33-5]: 0.10%; N-methyl-2-pyrrolidinone[872-50-4]: 4.00%; Surfynol 440 [9014-85-1]: 0.40%; butyl carbitol[112-34-5]: 6.00%; glycerol [56-81-5]: 8.00%; diethylene glycol[11-46-6]: 8.00%; and a blue fluorophore, e.g. Lake Placid Blue coreshell Evidots (SG-CdSe—ZnS-Tol-05-490-04, available from EvidentTechnologies, Inc., Troy, N.Y.): 2.50%. Angstrom SC-5 (available fromAngstrom Technologies, Inc. of Erlanger, Ky.), and Tinopal SFP,[41098-56-0] (available from Ciba, Inc. of Tarrytown, N.Y.) are alsosuitable as substitutes for the blue fluorophore in this ink.

Example 4

Invisible white-fluorescent inks were formulated by mixing deionizedwater: 69.70%; Proxel GXL [2634-33-5]): 0.10%; N-methyl-2-pyrrolidinone[872-50-4]: 4.00%; Surfynol 440 [9014-85-1]: 0.40%; butyl carbitol[112-34-5]: 6.00%; glycerol [56-81-5]: 8.00%; diethylene glycol[11-46-6]: 8.00%; and a white fluorophore: 3.80% total consisting ofsuitably weighted combinations of red, blue, and green (and/oryellow-green or yellow) fluorophores. Organic white fluorophores, suchas Angstrom SC-16 (available from Angstrom Technologies, Inc. ofErlanger, Ky.) may also be used to make fluorescent inks for use in thepresent invention. Suitable yellow fluorophores, such as Angstrom SC-19,SC-19D, SC-6 and SC-27, combined with suitable blue fluorophores, suchas SC-5, SC-17, SC-18, SC-29L, SC-11, SC-28 and/or SC-26D, may also beused to make inks with white fluorescent emissions.

Such a white invisible ink may be used to print a black and white image,such as the aforementioned barcodes and/or the image illustrated in FIG.8. In other embodiments, red, green (or yellow-green or yellow), andblue color fluorescent inks of the present invention may be combinedwith suitable weighting to print a black and white image.

Other fluorophores suitable for use in the present invention can be oforganic or inorganic composition, with a variety of emission colors.Some desirable characteristics of the UV-fluorescent materials used tomake invisible inks include: preferably having a high extinctioncoefficient, a good quantum yield, and fluorescent emission in thedesired color range. Suitable particle size (when pigments rather thandyes are used) is also a desirable characteristic. For a fluorescentmaterial to be useful with most of the commercially available inkjetprinters the particle size should be less than one micrometer,approximately. Lightfastness and chemical compatibility are desirable interms of longevity and durability of the printed image. The desiredexcitation characteristics of the UV-fluorescent fluorophores include anarrow spectral line width specific for either short- and/or long-waveUV light, depending on the desired effect, and a high extinctioncoefficient.

Among the many different fluorophores useful in this invention are: thebenzoxazoles of Angstrom SC-138(2,5-Bis-benzooxazol-2-yl-benzene-1,4-diol); Angstrom SC-164(4-Benzooxazol-2-yl-2,5-dihydroxy-benzoic acid methyl ester); and/orAngstrom SC-166 (4-Benzooxazol-2-yl-2,5-dihydroxy-benzoic acid). Thesefluorophores all emit in the red region (580-650 nm). See the structuresfor these compounds below, which are referenced using the above Angstromnumbers. These compounds were named according to IUPAC rules, usingAutoNom Version 2.1, Beilstein GmbH, and illustrated using ChemDrawUltra, Version 6.0.1© 2000, CambridgeSoft.com, Cambridge, Mass.).

NIR (Near Infrared)/IR-fluorescent materials suitable for use in thepresent invention include components with various excitation andemission characteristics, such as UV excitation to NIR/IR emission,visible excitation to NIR/IR emission, NIR/IR excitation to UV emission,UV excitation to NIR/IR and visible emission, and/or NIR/IR excitationto visible and NIR/IR emission. Some of these materials are inorganic innature; however, organic IR-fluorescent materials may be satisfactorilyemployed. In this regard, the use of quantum dots that fluoresce in theNIR or IR region may be used in one embodiment of the invention, asdescribed in more detail below. Dyes or pigments may be used, with theparticle size as a limitation that should be considered. As with mostmaterials useful in inkjet printing, the particle size of the pigment(s)should typically be less than or equal to about one micrometer.

The use of NIR/IR-fluorescent materials for security printing iswell-documented and is described in the following patents, which areincorporated herein by reference in their entirety: U.S. Pat. No.5,614,008 by Escano, et al. and U.S. Pat. No. 5,093,147 by Andrus, etal. Other examples of NIR/IR-fluorescent materials used for securityprinting include IR-Core PbSe Evidots [1306-24-7] (Available fromEvident Technologies, Inc. of Troy, N.Y.), IR-144 [54849-69-3](Available from Fisher Scientific Inc. of Pittsburgh, Pa.),3,3′-Diethylthiadicarbocyanine iodide [514-73-8] (Available fromSigma-Aldrich Chemical Co. of St. Louis, Mo.), NIR-667 [163016-50-0](Available from Sigma-Aldrich Chemical Co. of St. Louis, Mo.), NIR-664[167638-53-1] (Available from Sigma-Aldrich Chemical Co. of St. Louis,Mo.). The following cyanine-type, NIR/IR fluorophores are commerciallyavailable from Licor, Inc. of Lincoln, Nebr.: IRD-41, IRD-700, IRD-800,and CY-5. Pyrilium-type NIR/IR fluorophores, such as those described inthe paper by G. A. Reynolds, “Stable Heptamethine Pyrylium Dyes ThatAbsorb in the Infrared”, Journal of Organic Chemistry, V. 42, No. 6(1977), pp. 885-888 are also useful in the present invention. Theseexamples represent a few of the many types of NIR/IR fluorophores thatare preferred for use with this invention.

While the use of IR-fluorescent materials provides satisfactory resultsin many applications, many types of IR-absorbing materials, eitherpigments and/or dyes, such as Keysorb 990NM, 992NM, 993NM, and others ofthis series available from Keystone Aniline Corporation of Chicago,Ill., are also useful.

As described above, the inks of the present invention may provide NIR,IR UV and visible light fluorescent emission in response to any of NIR,IR, and UV excitation energy, and may provide NIR, IR and UV fluorescentemission in response to any of NIR, IR UV and visible spectrumexcitation energy. Often, but not always, the excitation energy willhave a wavelength that is different than that of the emission energy. Insome cases, IR-absorbing pigments and dyes may be used in the inks ofthe present invention, as discussed above.

In some applications, it may be desirable to provide an ink of firstcolor in the red, green, blue set with fluorescent emission in onewavelength range, e.g., visible spectrum, and provide an ink of a secondcolor in this set with fluorescent emission in a different wavelengthrange, e.g., IR. A third ink in the set could have a fluorescentemission in yet another wavelength range, e.g., NIR. The inks may becaused to fluoresce in response to excitation radiation of a singlewavelength or range of wavelengths, or each ink may be chosen so as tofluoresce in response a particular excitation radiation wavelength orrange of wavelengths. Thus, the present invention is not limited tocolor fluorescent emission, as NIR/IR and UV emission are not in thevisible spectrum.

Fluorophore microparticles and other microparticles having sizes notresolvable by the unaided human eye may be incorporated into the inks.Such microparticles may have diameters of about one micrometer or less,and are useful as secondary authentication features. They are simple toauthenticate but extremely difficult for a counterfeiter to reproduce.The microparticles are typically coded by visible color bands and/orchemical signature tagging. These materials are commercially availablefrom sources such as Microtrace, LLC and Tracking Technologies, Inc.,both of Minneapolis, Minn., and are described in U.S. Pat. No. 6,647,649to Hunt et al., which is incorporated herein by reference. Typically,the microparticles will constitute a fraction of a percent up to 25weight percent of the ink composition. Some particle sizes that arecurrently commercially available, about 20 microns, are not useful ininkjet printing methods. However, they are useful when incorporated intolaminate films, onto which the inkjet image is printed, and/or whenincorporated into films that cover the inkjet image. These materials canalso be sprayed onto a printed surface, without affecting the emissioncharacteristics of the other inks of the present invention. While theuse of microparticles in pigmented fluorescent coatings is known, asdescribed in U.S. Published Application No. US20020066543A1, the use ofsuch particles in fluorescent inkjet inks of the present inventionrepresents an important advance in the field of such inks andfluorescent image indicia.

Semiconductor nanocrystals, or quantum dots, or quantum rods are verysmall particles ranging in size from a few atoms to hundreds of atoms indiameter. The unique properties of quantum dots result from quantum-sizeconfinement, which occurs when the semiconductor particles are smallerthan their exciton Bohr radii. These materials can be made from avariety of materials using various methods and can be engineered toexhibit particular properties such as dispersion characteristics,reactivity (through the addition of organic functionality), and emissionwavelength. Suitable compositions and preparation methods are describedin the papers by A. P. Alivisatos et al., “Semiconductor Clusters,Nanocrystals, and Quantum Dots,” Science, V. 271 (1996), pp. 933-937; byM. G. Bawendi, et al., “Synthesis and Characterization of NearlyMonodisperse CDE (E=S, Se, Te) Semiconductor Nanocrystallites,” Journalof the American Chemical Society, V. 115 (1993), pp. 8706-8715; and A.J. Nozik et al., “Synthesis and Characterization of InP, GaP, and GaInP₂Quantum Dots,” Journal of Physical Chemistry, V. 99 (1995), pp.7754-7759, each of which is incorporated herein by reference in itsentirety.

An example of the synthesis of ZnS-capped CdSe quantum dots, adaptedfrom M. A. Hines, et al., “Synthesis and Characterization of StronglyLuminescing ZnS-Capped CdSe Nanocrystals,” Journal of PhysicalChemistry, V. 100 (1996), pp. 468-471; is presented below in Example 5for illustration purposes, and is incorporated herein by reference inits entirety.

Example 5

The following organometallic synthesis of CdSe/ZnS quantum dots can beused to create quantum dots suitable for inclusion in the inks of thepresent invention. Stock solutions of Cd and Se can be prepared in anN₂-filled drybox by dissolving 0.2 g (2.5 mmol) Se in 4.5 mL oftri-n-octylphosphine (TOP). Me₂Cd (0.25 mL, 3.5 mmol) can be added tothe TOP-Se and diluted with 19.5 mL of TOP. The Zn and S stock solutioncan be similarly prepared with 0.52 mL of (TMS)₂S (2.5 mmol) in 4.5 mLof TOP, adding 3.5 mL of Me₂Zn solution (3.5 mmol) and diluting with 16mL TOP. These stock solutions are then used in the following synthesis:12.5 g of tri-n-octylphosphine oxide (TOPO) is heated to 200° C. undervacuum, at which temperature it is dried and degassed for approximately20 min. The temperature is then raised to 350° C. under approximately 1atm. of argon. Once the temperature is stabilized, 0.7 mL (0.07 mmol Se,0.1 mmol Cd) of CD/Se/TOP stock solution is injected into the reactionvessel, and the heat removed. The reaction vessel is allowed to cool toapproximately 310° C., at which point an aliquot is taken for analysis.When the temperature reaches 300° C. the ZnS/TOP solution is injected infive 0.55 mL portions at approximately 20 sec. intervals. A total moleratio of injected reagents is 1:4 Cd/Se:ZnS. Upon cooling, the reactionmixture is stirred at 100° C. for 1 h. The nanocrystals can be purifiedby precipitation with anhydrous methanol, centrifuging and subsequentlywashing with the methanol (3×) to remove any residual TOPO.

There are many ways to functionalize the exterior of the nanocrystals toimprove the chemical, and photochemical, stability; solubility;reactivity; etc. which make these nanocrystalline fluorophoresparticularly amendable for use in the current invention. The methoddescribed above involves ZnS surface-coated nanocrystals, although inmany cases in the present invention it will be desirable to match thesurface chemistry of the nanocrystal to that of the ink, the particularapplication characteristics, and/or other desired properties. Examplesof possible surface modifications would include encapsulation intopolymer mixtures in the form of microspheres, or other polymercomposites, as described in the paper by S. Farmer, et al., “Synthesisof Luminescent Organic/Inorganic Polymer Nanocomposites”, PolymericMaterials Science and Engineering, V.82 (2000), pp. 237-238. Theaddition of a functionalizable, water-soluble siloxane shell, asdescribed in the paper by A. P. Alivisatos et al., “Synthesis andProperties of Biocompatible Water-Soluble Silica-Coated CdSe/ZSSemiconductor Quantum Dots,” Journal of Physical Chemistry B, V. 105(2001), pp. 8861-8871, is another type of surface modification for thenanocrystal fluorophores. Yet another type of surface modification,described in the paper by X. Peng, et al., “Stabilization of InorganicNanocrystals by Organic Dendrons”, Journal of the American ChemicalSociety, V. 124 (2002), pp. 2293-2298, involves the binding of organicdendron ligands onto the nanocrystal surface.

The methods of surface modification described in the articles referencedabove are just a few examples of the numerous methods available formodification of the semiconductor nanocrystal fluorophores. Anotherapproach for altering fluorescent nanocrystals to improve their use forvarious applications, including inkjet printing methods, is describedimmediately below. In this approach, CdSe/ZnS core/shell nanocrystalssynthesized in TOPO are silica coated to make them water soluble,providing enhanced photochemical stability, and thus better suitable foruse in water-based inkjet inks. The following silica-coating procedureis easily scaled and applicable for making silica-coated CdSe/ZnSnanocrystals from approximately 2 to 8 nm in size.

One mL of nanocrystals in butanol/TOPO (optical density ˜2) wasprecipitated with anhydrous methanol. The wet precipitate was dissolvedin 50 μL of mercaptopropyltris(methoxy)silane (MPS). After vortexing, 5μL of tetramethylammonium hydroxide (TMAH) in methanol was added, andthe solution became optically clear. This mixture was diluted with 120mL of anhydrous methanol, basified to a pH of approximately 10 with 750μL of TMAH, and placed under N₂ in a 500 mL three-neck flask. After 1 hof stirring, the solution was gently heated to approximately 60° C. for30 min. After cooling to room temperature (RT), 90 mL of methanol, 10 mLof 18 MΩ Millipore (Millipore, San Jose, Calif.) water, 600 μL of(trihydroxysilyl)propyl methylphosphonate and 20 μL of MPS were added,stirred for approximately 2 h, heated to ˜60° C. for less than 5 min,and cooled to ˜30° C. The remaining silanol groups were quenched with amixture of 20 mL methanol and 2 mL of chlorotrimethylsilane basifiedwith ˜3 g of solid TMAH pentahydrate, and then stirred again for ˜2 h.The solution was heated to ˜60° C. for 30 min, and left at RT for 2-4days while stirring in a N₂ atmosphere.

In the next step, the solution was condensed by a factor of 2-5 in arotary evaporator and left again for 24 hours. At this point thesolution was dialyzed in a 10,000 MWCO dialysis tubing against methanolfor a day, and subsequently filtered through a 0.45 μm pore size nylonsyringe filter. The excess of free silane was removed by condensing thesolution using centrifugal filter devices. The volume of the solutionwas reduced to about 2 mL, and this solution was left for at least 12 hbefore being passed through a solvent exchange column NAP columns or a“homemade” 20 cm long column with a 0.7 cm diameter filled with ˜5 g ofSephadex G25 medium and equilibrated with 10 mM PB buffer, pH ˜7 wereused to obtain an eluted solution. The eluted solution was monitored byfluorescence and only the fluorescent fraction was collected. It wasleft a few hours and then filtered through a 0.22 mm pore size acetatefilter. As an optional step, this solution was further dialyzed against18 MΩ Millipore water for 1-4 days in a 10,000 MWCO membrane, runthrough a 0.22 mm pore size filter, and concentrated to a desiredconcentration in a vacufuge concentrator at 60° C. (Eppendorf #5301,Westbury, N.Y.).

As a last step, the solution was centrifuged at 20000×g for 30 min andthe precipitate was discarded. The supernatant was stored in air withtypical OD ˜0.3-1 at the absorption feature, corresponding to aconcentration of 3-10 μM (extinction coefficient assumed to be 10⁵ M⁻¹cm⁻¹).

Quantum dots are also commercially available from sources such asQuantum Dot Corporation of Hayward, Calif., or Evident Technologies,Inc. of Troy, N.Y. These materials are appropriate for inkjet printingbecause of the small particle sizes and ease of dispersion in water orother solvents, after desired surface modification(s). The use ofquantum dots for security markings offer many advantages in that theyexhibit high fluorescence intensity, a high quantum yield, a narrowfluorescent emission, and have excellent stability and lightfastness.Typically, the quantum dots will constitute 0.01%-25% (by weight) of theink composition.

Because quantum dots may be engineered to have selected properties, theymay fulfill multiple purposes when included in the fluorescent inks.Quantum dots may be used as the source of the fluorescent color(s),i.e., as the fluorophore, in the ink. Alternatively, or in addition,quantum dots may be used to provide a unique fluorescent signature inthe ink. A unique fluorescent signature could be obtained, for example,by using quantum dots having a fluorescent emission that differs in aselected manner, e.g., spectral linewidth, or fluorescent emission, fromthe fluorophore in the ink having the same or different fluorescentemission wavelength as the quantum dots.

Referring now to FIG. 9, a resulting color gamut 120 of emissions of aset of fluorescent inks made in accordance with the present invention isshown. This set of fluorescent inks includes both common fluorophoresand/or quantum dots as the fluorescent component. Color gamut 120 isindicated by the CIE 1931 chromaticity coordinates describing a planecomprising the following (X,Y coordinate) points of approximately,(+/−0.05): (0.1, 0.7) (0.16, 0.17) (0.23, 0.008) (0.62, 0.27) (0.46,0.5).

Other additional authentication features may be included in images andmethods of the present invention. In some cases it may be desirable toinclude scent in one or more of the image layers. Exemplary compositionsand materials to produce scent include esters, such as butyl acetate(banana scent), methyl salicylate (wintergreen). and many other uniquescents, like benzaldehyde (cherry), and/or phenylethanol (rose). Thesescents are in general pleasurable, however, unpleasant scents, such asputracene (decaying flesh), mercaptoethanol (rotten eggs), etc. may alsobe used. Virtually any scent can be added to an ink, in a soluble form,however, encapsulated scent markers may also be used. Chemical taggants(other than quantum dots and microparticles, to the extent considered“chemical taggants”) may also be used as authentication features.Suitable chemical taggants include, without limitation, any chemicalthat can be authenticated; any chemical that contains a unique element,or structural element, found few other places, such as deuterium,tritium, gadolinium (Gd), and/or terbium (Tb); structural elements suchas crown ethers, rotaxanes, and linear alkanes of a sort that can beauthenticated through the presence of specific patterns detectable bymass spectrometry. In some cases, it may also be desirable to useimmunochemical taggants such as specific complimentary antigens andantibodies.

Materials having electromagnetic radiation emission in wavelength rangesother than NIR, IR, visible spectrum and UV, e.g., X-ray and shortwaveRF, may also be employed as secondary authentication features. In somecases these alternative materials may provide a continuous emission andin other cases will emit only in response to appropriate excitationenergy. Other authentication features include the use of maskingelements, described immediately below, and the use of microparticles inthe ink compositions. The latter methods are described above in thesection titled “Ink Compositions.”

In the masking methods, at least one of the multiple chromophoresincluded in the fluorescent inks is not intended to contribute to visualappearance of the image but instead selectively masks fluorescent lightfrom one or more of the other chromophores. With suitable selection ofsuch a masking chromophore and a corresponding optical filter, themasking fluorescence can be filtered out to allow authentication usingthe resulting unmasked color combinations from the other fluorescentchromophores.

Thus, in this embodiment, the ink formulations may include a fluorescentcompound in an amount that, when printed, will serve to mask one ormore, or all of the other fluorescent colors. This masking component mayfluoresce with a bright blue color, for example. This may also be donewith a second printing pass using a masking-type cartridge in a singlecolor slot and printing a solid single-color layer over the previousimage. This may be accomplished by inclusion of the masking chromophoreinto a specific ink, or inclusion into an entire set of inks, the use ofan overlaid film, and/or by overprinting of the original invisiblefluorescent image using an offset printing method with an overprintvarnish of a single fluorescent color, or many other possible methods ofapplication. For example, in this method, a secondary image may becreated that will fluoresce in a bright blue color with a peak emissionat about 420 nm, which hides the original multi-color image. Theoriginal image is then detectable through the use of awavelength-selective filter or combination of filters.

As mentioned above, the present invention includes the use of multipleauthentication features in connection with an image. The multipleauthentication features may, for the purposes of explanation, and notlimitation of the invention, be categorized as primary, secondary andtertiary features. Primary authentication features are the imagesprovided by the image layers making up the authentication image, asdiscussed above.

Secondary authentication features provide information, in many forms,that is included in one or more of the image levels. Secondaryauthentication features included in one image level may be, but are notnecessarily, excluded from the other image levels. The present inventionencompasses as a secondary authentication feature virtually any compoundor material that provides information that can be detected, whether byunaided human faculties or with the use of detection equipment. Withoutlimiting the invention, examples of secondary authentication featuresdiscussed above include scent, microparticles, quantum dots and otherchromophores (fluorophores) having distinguishable emission attributessuch as wavelengths, line widths, intensities, and decay times offluorescent light emission.

Tertiary authentication features include patterns or relationshipsbetween primary features, between primary features and secondaryfeatures and/or between secondary features. For example, one tertiaryauthentication feature could be the combination of an apple as theprimary image and red emission at 620 nm and a banana scent. As anotherexample, one image layer could be designed to have a fluorescent IRemission with attributes that, in combination with attributes from avisible spectrum emission from a second image layer, create acombination of attributes constituting a tertiary authenticationfeature. Thus, a tertiary authentication feature is not a component ofthe fluorescent inks of the present invention, but rather is a patternor relationship between discernable attributes of the primary andsecondary authentication features. As those skilled in the art willappreciate, there are a large number of tertiary authentication featuresthat can be developed and used. Tertiary authentication features can bedeveloped so as to be detectible with unaided human faculties, with onlymachines, including computer hardware and software, or with acombination of the two.

To use tertiary authentication features in connection withauthentication of an article, the tertiary authentication feature isfirst defined, the primary and secondary authentication features arecreated so as to include the tertiary authentication feature. Then, atthe time of authentication, a check is made for the pattern orrelationship of the tertiary authentication feature. The presence of thetertiary authentication feature suggests authenticity and its absenceindicates forgery.

Thus, an overall method in accordance with the invention for marking anarticle with image indicia, includes providing a plurality of inkjetinks having a plurality of fluorescence colors under illuminationoutside the visible spectrum and substantially invisible underillumination within the visible spectrum, converting the color indiciato be printed to a color negative form, separating the colors of theimage indicia into a plurality of image levels in accordance with thefluorescence colors of the inks, using an inkjet printer intended foruse with subtractive-color ink containers (replacing eachsubtractive-color ink container with a container containing thecomplementary color among the fluorescent inks) and printing each imagelevel in mutual registration on the article using the corresponding ink.The printed indicia may be used for authentication, information, ordecoration, for example.

The methods of the invention may be facilitated by providing a set ofinkjet containers including (1) a first ink container carrying inkinvisible under ordinary white-light illumination, but fluorescent witha color complementary to cyan, (2) a second ink container carrying inkinvisible under ordinary white-light illumination, but fluorescent witha color complementary to magenta, and (3) a third ink container carryingink invisible under ordinary white-light illumination, but fluorescentwith a color complementary to yellow.

A fourth ink container carrying black ink may also be provided in theset or provided separately. The three containers of the set carryingred, green, and blue fluorescent inks may be labeled accordingly, as“Replaces cyan ink cartridge” for the cartridge carrying red-fluorescentink, “Replaces magenta ink cartridge” for the cartridge carryinggreen-fluorescent ink, and “Replaces yellow ink cartridge” for thecartridge carrying blue-fluorescent ink.

The invention is useful for marking articles with image indicia forauthentication, information, or decoration, wherever a number ofinvisible fluorescent inks are needed. Inkjet printing can be used withthe inks to create color images, both visible and invisible, that areuseful in security printing. The present invention illustrates methodsof printing that adapt emissive, or additive, colors derived from theuse of fluorescent materials to create images, including full colorimages, with technology such as printers and software that is commonlyused to create reflective color images. A number of security methods,useful separately and/or in combinations use multiple authenticationfeatures that allow for visual and machine authentication of securitymarks. These methods can be used with virtually any commerciallyavailable or industrial inkjet printer, including those that usethermal, piezo, drop-on-demand, and continuous piezo types of inkjetprinting.

Although the foregoing has been a description and illustration ofspecific embodiments of the invention, various modifications, additions,and changes can be made thereto by persons skilled in the art withoutdeparting from the scope and spirit of the invention as defined by thefollowing claims. For example, a single emission color of a particularsecurity mark may serve mainly as a location device to point the user tothe exact location of additional, and/or machine-read, security marks.In another example, an invisible, full-color image, able to be seen onlyunder UV irradiation, is used as a primary security mark, whileadditional marks, such as IR-fluorescent compounds, and/or additionalUV-fluorescent compounds, and/or microparticle taggants, and/or otherchemical taggants, etc., are included within the invisible, full-colorimage to serve as secondary, tertiary, and additional security features.

Although the invention has been described and illustrated with respectto exemplary embodiments thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, without partingfrom the spirit and scope of the present invention.

1. An emissive image printing system for printing an image on a substrate, the image being emissively perceptible, the system comprising: a red additive-color emissive ink having a red emissive component with a dominant emissive wavelength between about 590 nanometers and about 680 nanometers when exposed to an excitation energy, the red emissive component being substantially invisible under illumination within the visible spectrum when said red additive-color emissive ink is printed as part of an image indicia on a substrate; a green additive-color emissive ink having an green emissive component with a green dominant emissive wavelength between about 500 nanometers and about 550 nanometers when exposed to the excitation energy, the green emissive component being substantially invisible under illumination within the visible spectrum when said green additive-color emissive ink is printed as part of the image indicia; and a blue additive-color emissive ink having an blue emissive component with a blue dominant emissive wavelength between about 420 nanometers and about 480 nanometers when exposed to the excitation energy, the blue emissive component being substantially invisible under illumination within the visible spectrum when said blue additive-color emissive ink is printed as part of the image indicia, the red, green, and blue additive-color emissive inks being configured to be printed to a substrate using an ink printer device intended for use with subtractive-color ink.
 2. A system according to claim 1, further comprising a subtractive-color ink printer intended for use with subtractive-color ink cartridges and wherein said red, green, and blue additive-color emissive inks are in one or more ink cartridges configured to work with the subtractive-color ink printer.
 3. A system according to claim 2, wherein said subtractive-color ink printer includes a subtractive black-color ink head that is disabled for printing using said red, green, and blue additive-color emissive inks.
 4. A system according to claim 1, further comprising a subtractive-color ink printer intended for use with subtractive-color inks and wherein said red, green, and blue additive-color emissive inks are included in one or more ink containers configured to work with the subtractive-color ink printer.
 5. A system according to claim 4, wherein said subtractive-color ink printer includes a subtractive black-color ink head that is disabled for printing using said red, green, and blue additive-color emissive inks
 6. A system according to claim 1, further comprising a computer device programmed to convert an image to be printed using the red, green, and blue additive-color emissive inks into a color negative form.
 7. A system according to claim 1, further comprising a machine readable hardware storage medium containing machine readable instructions for converting an image to be printed using the red, green, and blue additive-color emissive inks into a color negative form.
 8. A system according to claim 1, wherein one or more of said red, green, and blue additive-color emissive inks includes a secondary emissive component that is in addition to the corresponding red, green, and blue components.
 9. A system according to claim 8, wherein a first one of said red, green, and blue additive-color emissive inks includes a secondary emissive component that emits in the visible spectrum; a second one of said red, green, and blue additive-color emissive inks includes a secondary emissive component that emits in the infrared spectrum; and a third one of said red, green, and blue additive-color emissive inks includes a secondary emissive component that emits in the near-infrared spectrum.
 10. A system according to claim 8, wherein at least one of said red, green, and blue additive-color emissive inks includes a secondary emissive component that emits in the infrared spectrum.
 11. A system according to claim 1, wherein at least one or more of said red, green, and blue additive-color emissive inks includes a secondary authentication feature that is in addition to said red, green, and blue emissive components, the secondary authentication feature including a feature selected from the group consisting of, a quantum dot material, a functionalized nanocrystal material, a semiconductor nanocrystal material, a quantum rod material, a chemical signature tagging material, and any combinations thereof.
 12. A system according to claim 1, wherein said red emissive component when printed on the substrate includes a component having CIE 1931 chromaticity coordinates of about (+/−0.05): (0.48, 0.22) (0.48, 0.43), and (0.67, 0.26); said green emissive component when printed on the substrate includes a component having CIE 1931 chromaticity coordinates of about (+/−0.05): (0.14, 0.42) (0.12, 0.72), and (0.43, 0.46); and said blue emissive component when printed on the substrate includes a component having CIE 1931 chromaticity coordinates of about (+/−0.05): (0.16, 0.10) (0.15, 0.38), and (0.30, 0.15).
 13. An emissive image printing system for printing an image on a substrate, the image being emissively perceptible, the system comprising: a red additive-color emissive ink having a red emissive component with a dominant emissive wavelength between about 590 nanometers and about 680 nanometers when exposed to an excitation energy, the red emissive component being substantially invisible under illumination within the visible spectrum when said red additive-color emissive ink is printed as part of an image indicia on a substrate; a green additive-color emissive ink having an green emissive component with a green dominant emissive wavelength between about 500 nanometers and about 550 nanometers when exposed to the excitation energy, the green emissive component being substantially invisible under illumination within the visible spectrum when said green additive-color emissive ink is printed as part of the image indicia; a blue additive-color emissive ink having an blue emissive component with a blue dominant emissive wavelength between about 420 nanometers and about 480 nanometers when exposed to the excitation energy, the blue emissive component being substantially invisible under illumination within the visible spectrum when said blue additive-color emissive ink is printed as part of the image indicia, wherein the red, green, and blue additive-color emissive inks are configured to be printed to a substrate using an ink printer device intended for use with subtractive-color ink; a computer device programmed to convert an image to be printed using the red, green, and blue additive-color emissive inks to a color negative form; and a subtractive-color ink printer intended for use with subtractive-color ink, wherein the red, green, and blue additive-color emissive inks are configured to be printed to a substrate using the subtractive-color ink printer.
 14. A system according to claim 13, further comprising a machine readable hardware storage medium containing machine readable instructions for converting an image to be printed using the red, green, and blue additive-color emissive inks into a color negative form.
 15. A system according to claim 13, wherein one or more of said red, green, and blue additive-color emissive inks includes a secondary emissive component that is in addition to the corresponding red, green, and blue components.
 16. A system according to claim 15, wherein a first one of said red, green, and blue additive-color emissive inks includes a secondary emissive component that emits in the visible spectrum; a second one of said red, green, and blue additive-color emissive inks includes a secondary emissive component that emits in the infrared spectrum; and a third one of said red, green, and blue additive-color emissive inks includes a secondary emissive component that emits in the near-infrared spectrum.
 17. A system according to claim 15, wherein at least one of said red, green, and blue additive-color emissive inks includes a secondary emissive component that emits in the infrared spectrum.
 18. A system according to claim 13, wherein at least one or more of said red, green, and blue additive-color emissive inks includes a secondary authentication feature that is in addition to said red, green, and blue emissive components, the secondary authentication feature including a feature selected from the group consisting of, a quantum dot material, a functionalized nanocrystal material, a semiconductor nanocrystal material, a quantum rod material, a chemical signature tagging material, and any combinations thereof.
 19. A system according to claim 13, wherein said red emissive component when printed on the substrate includes a component having CIE 1931 chromaticity coordinates of about (+/−0.05): (0.48, 0.22) (0.48, 0.43), and (0.67, 0.26); said green emissive component when printed on the substrate includes a component having CIE 1931 chromaticity coordinates of about (+/−0.05): (0.14, 0.42) (0.12, 0.72), and (0.43, 0.46); and said blue emissive component when printed on the substrate includes a component having CIE 1931 chromaticity coordinates of about (+/−0.05): (0.16, 0.10) (0.15, 0.38), and (0.30, 0.15).
 20. An emissive image printing system for printing an image on a substrate, the image being emissively perceptible, the system comprising: a subtractive-color ink printer intended for use with subtractive-color ink; a red additive-color emissive ink having a red emissive component with a dominant emissive wavelength between about 590 nanometers and about 680 nanometers when exposed to an excitation energy, the red emissive component being substantially invisible under illumination within the visible spectrum when said red additive-color emissive ink is printed as part of an image indicia on a substrate, said red additive-color emissive ink included in a container configured to replace a cyan-colored subtractive ink container of the subtractive-color ink printer; a green additive-color emissive ink having an green emissive component with a green dominant emissive wavelength between about 500 nanometers and about 550 nanometers when exposed to the excitation energy, the green emissive component being substantially invisible under illumination within the visible spectrum when said green additive-color emissive ink is printed as part of the image indicia, said green additive-color emissive ink included in a container configured to replace a magenta-colored subtractive ink container of the subtractive-color ink printer; a blue additive-color emissive ink having an blue emissive component with a blue dominant emissive wavelength between about 420 nanometers and about 480 nanometers when exposed to the excitation energy, the blue emissive component being substantially invisible under illumination within the visible spectrum when said blue additive-color emissive ink is printed as part of the image indicia, said blue additive-color emissive ink included in a container configured to replace a yellow-colored subtractive ink container of the subtractive-color ink printer; and a computer device programmed to convert an image to be printed using the red, green, and blue additive-color emissive inks to a color negative form and to use the subtractive-color ink printer to print the image using the color negative form and said red, green, and blue additive-color emissive inks. 